1. Field of the Invention
The present invention relates to an apparatus for investigating the concentration of a material by means of optodes.
2. Description of the Prior Art
The term "optode" is used hereinafter to denote an optometric device comprising wall means which define an indicator chamber, the wall means including at least one transparent wall portion, and the indicator chamber containing an indicator substance which is effective to modify the spectral characteristics of light incident thereon. It is known to use an optode to investigate the concentration of a material in a space containing the material. In this case, the wall means of the optode include a permeable wall portion, i.e. a wall portion through which the material under investigation can diffuse, and the optode is disposed with this permeable wall portion facing the space containing the material; and the indicator substance is selected so that the modification effected in the spectral characteristics of light incident thereon is dependent upon the concentration of the material under investigation in the indicator chamber.
The term "measuring indicator substance" or "measuring indicator" is used hereinafter to denote an indicator substance which is effective to modify the spectral characteristics of light incident thereon in a manner dependent upon the concentration of a material under investigation in the indicator chamber, and the term "measuring optode" is used hereinafter to denote an optode having a permeable wall portion and containing a measuring indicator substance.
Now, oftentimes the only measuring indicators are available are those which under influence of the material under investigation change only the intensity of the spectral distribution. In such case quantitative measurements are impossible if the concentration of the indicator, other optically caused changes of intensity or electronic changes, e.g. the amplification or gain do not enter definably into the resulting measurement values. Therefore, a large number of fluorescence-, absorption-, reflection-, and luminescence indicators cannot be utilized for such measurements. In particular, it is not possible by use of measuring microoptodes or nanooptodes, i.e. measuring optodes having a diameter less than 10 .mu.m, which can be added to a carrier substance, to determine the concentration of the optodes or the relative concentration of the optodes.